本例演示月亮、地球和太阳之间的相对运动（公转、自转）关系，由于地球绕太阳旋转一周则月亮绕地球旋转12周的自然规律-This example demonstrates, relative movement between the earth and the sun, the moon (orbit, rotation), as the earth goes around the earth makes one revolution around the sun, the moon for 12 weeks of nature